The Internet of Things (IoT) refers to a collection of sensors having network connectivity to allow the distributed collection and exchange of data. Massive deployment of a large number of IoT devices to connect to existing wireless wide area networks (WWANs) operating in accordance with a Third Generation Partnership Project (3GPP) may present new problems that should be addressed. Evolved Packet Core (EPC) signaling may experience overload due to frequent state changes between the two current network states, the connected state (EMM_Connected) and the idle state (EMM_Idle). Furthermore, many IoT devices are not connected to power, and therefore should operate with very efficient battery usage. In addition, IoT devices may transmit smaller bursts of data at more frequent intervals, the delay for uplink transmissions should be very low delays. Although some of these issues may be addressed under current architectures, the issues are not all addressed simultaneously.
One approach may be to keep the IoT user equipment (UE) permanently in a connected state such as in EMM_Connected or RRC_CONNECTED, in order to address the signaling load due to state transitions and provide low uplink delays. This approach, however, would have a huge impact on battery life because the UE continuously performs measurements to support the Handover procedure, and because radio interface signaling involves performing the handover at every cell change. Also, while the EPC signaling load due to state transitions is reduced, a different type of EPC signaling load, due to frequent handovers, may be created.
The impact on battery life due to a permanent RRC_CONNECTED state may be somewhat mitigated by using longer values for Connected mode discontinuous reception (DRX) cycle (C-DRX cycle), but this approach is likely to degrade the handover performance. Namely, in cases where the UE is moving very fast, the likelihood of handover failure increases because the serving cell signal becomes weaker as the target cell signal gets stronger, and hence the handover (HO) command sent by the serving cell may not successfully be received. The use of a longer C-DRX cycle will only increase the handover failure rate because in the interest of power saving, the UE performs measurements only during the receiving occasion of the C-DRX cycle and hence a longer C-DRX cycle results in less frequent measurements.
In the case of a handover failure, the UE will declare radio link failure (RLF) and more signaling will be involved. The case of radio link failure (RLF) indicates that the UE performs an RRC connection reestablishment, which involves at least three messages over the air interface, and additionally there may be a delay to declare radio link failure during handover such as delay from expiry of the RLF timer. Moreover, subsequent to RLF, the UE has control over selecting the new cell, which means the network has no control over cell selection.
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